“Rubbery Stiffening” and Rupture Behavior of Freely Standing Nanometric Thin PIB Films

Abstract

Prior bubble inflation studies have shown strong evidence of rubbery-like stiffening behaviors for several organic and inorganic thin films. The possible origin is still unclear, but recently Ngai et al. [J. Polym. Sci., Part B: Polym. Phys. 2013, 51 (3), 214−224] and Li and McKenna [Macromolecules 2015, 48 (17), 6329−6336] proposed that the separation of molecular motions and dynamic fragility are closely related to the observed rubber-like stiffening behavior. In the present work, we report observations from bubble inflation measurements on nanometric thin polyisobutylene (PIB) films that test the correlations suggested by the Ngai coupling model (stiffening is related to the shape parameter describing the α-relaxation) and Li and McKenna (the rubbery stiffening correlates with the dynamic fragility). Mechanical properties and surface tension of nanometric thin PIB films were investigated through strain–stress measurements for film thicknesses ranging from 13 to 126 nm. The tests were performed at room ...